id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,testcase,blockedby,blocking,related,differential
5473,sortBy is no longer a good consumer in GHC 7,lpsmith,igloo,"The [http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/rewrite-rules.html#id717388 List Fusion section of the GHC User's Guide] lists {{{sortBy}}} as a good consumer.
In past versions of GHC, {{{sortBy}}} turned its input into a list of lists to be merged by using {{{map (:[])}}}, which is why it was a good consumer. However this is somewhat arguable, as it's only a good consumer in a weak sense of the word. When it comes to doing the real work of the algorithm, sort was never a good consumer.
However, in GHC 7, {{{sortBy}}} breaks its input into monotonic runs, producing a shorter outer list. This is not a good consumer in any sense of the word.
",bug,closed,normal,7.4.1,Compiler,7.2.1,fixed,,,Unknown/Multiple,Unknown/Multiple,Documentation bug,,,,,